As recent rapid trend in modern electronic devices is not only toward thinner, lighter and smaller devices, but also toward multifunctional and high-performance devices, the fabrication and technology of integrated circuits (ICs) has to evolve correspondingly toward a more high-density and miniature design so as to allow more electronic components to be received inside limited chip space. Consequently, the relating IC package substrate and the package technology are evolved accordingly to meet the trend.
To realize a package substrate with high-density circuit wires, the wires must be designed in a fine-pitch manner and often fabricated by the so-called “semi-additive process”. Whereby, the wire width and the wire separation between two adjacent wires are almost the same, for example, a width of 15 or 20 μm and a separation of 15 or 20 μm. As for such fine-pitch circuit wires, the wire thickness is usually at most 20 μm.
In the applications of high-power electronic product, the circuit wire should be thickened if possible to increase its cross-sectional area and hence its electrical conductivity. However, it is difficult to thicken wires in a fine-pitch circuit because that would lower fabrication yield and product reliability. Therefore it is in need of a new and advanced packaging solution.